Poison depedency

[happysalada]

You have a dependency on Poison.
Probably up until now, since Phoenix was using poison, it was working fine. The new Phoenix use Jason. So you will either need to specify the Poison dependency or switch to using Jason.

[scrogson]

Hi @happysalada,

This library only depends on Poison for tests, but it does set up the JSON serializer to use Poison by default and requires users to pull it in as a dependency.

I have this PR: #92 (which is over 1 year old) which changes the way serializers are registered.

I'll probably consider using Jason instead of Poison before I get around to pulling the trigger on merging it.

Thanks